Palladium dental alloy



Aug. 4, 1936. E. M/wlsE 2,050,077

PALLADIUM DENTAL ALLOY Filed Aug. l, 1954 2 Sheets-Sheet 2 l a" www l INVENTOR.

EDM UND N. W\SE wpwmkm, y

ATTORNEY.

Patented Aug. 4, 1936 p UNITED STATES i PATENT GFFICE Edmund M. wise, Westfield; N. J., assignor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application August 1,- 1934, SeriallNo. 737,896

ficiainis. (ci. lzas-134) The present invention relates to apalladium dental alloy and more particularly to'a dental y alloy containing palladium, gold, silverv and copper,

Heretofore, precious metal dental alloys-which Were used for cast or wrought structures con. tained large percentages of gold, say, about. 70% or more by weight in most cases. Frequently, `small amounts of silver and copper were added l to lower the melting point and to aiord amodcrate increase in hardness.' The harder alloys containedV platinumand in some cases lesser quantities of palladium were vused in conjunction therewith. 'I'he platinum functioned as a hardener and aided in increasing the response to heat -templates providing a precious metal dental .alloy treatment while the palladium tended to improve'the homogeneity of the alloy and to increase its melting point. It was generally believed that palladium, in contrast with platinum, softened 20 rather than hardened the' alloy and reduced its response to heat treatment. Many attempts were made to improve the precious metal dental al- .loys but proposals made thus far involved cer- 'y tain shortcomings including a deficiency in tarnish and corrosion resistance, a lack of 'strength and toughness and insuiiicient cheapness. f -As far as I am aware, no palladium dental alloy hasA been provided which is wholly satisfactory and successful in commercial use and which entirely meets the requirements of the situation. Ihave discovered that the prior notions regardling precious metal dental alloys, particularly with respect 'to"palladium, are unsound and I have 35, found that precious metal alloys containing palladium in substantial quantities when used in conjunction with proper proportions of gold, cop- .per and silver have remarkable properties and permity the saving of substantial quantities o f 40 gold. It is an object of the v.present inventiony to pro` vide a palladium dental alloy which is strong andtough and which possesses resistance to tarnish, to corrosion and to nitric acid. l

A further object of the invention is to provide a palladium dental alloy which can be easily cast and worked and which is responsive to age hardening. s p v It is also within the contemplation of the pres- 50 "ent'invention to provide a Dalladillmvdental allOy which can 'be made on an industrial scale, which can be handled, fabricated and worked with con` ventional appliances and equipment, and. which is relatively cheap and permits wide use.A

Other objects and advantages of the invention 5 will become apparent fromgth'e following description taken in commotion with the accompanying Y drawings in which:

Fig. 1 is a ternary diagram in whichthe present palladium .dental alloys ar`e plotted on the basis of weight percentages;'and' Fig. 2 is similar to Fig.' 1 with the exception that, the alloys are plotted on the basis of atomic percentages. .y

Generally speaking, the present invention con- 15 in which the palladium content (expressed in atomic percentage) is not less than40 nor more than 58% Lof the 'combined atomic percentages (26 to 43% of the combined weight percentages) 20 of gold rplus palladium, and the palladium content (expressed in atomic percentage) for maxic.;

,-mum strength isof 'the combined atomic percentage (35% of the'combined weight percentages) of gold plus palladium. 'I'he combined 25 atomic percentage. of gold plus palladiumvmay range between 30 gandfabout 55 atomic percent l (38.9 and' about 73.7 weight percent). When such variations are made the cost. and nobility increases Ywith the` percentage of gold plu'spa1 30 ladium. Increasing the percentage appreciably ab'ove 55 atomic per cent (73.7 Weight percent), particularly in cast alloys, results in alloys which do not age harden. The strength properties reach a maximum when 22.5 atomic per cent 35 (about v21 Weight per cent) palladium and 22.5 atomic per cent (about 39 weight per cent) gold are present, and such an alloy is very suitable for general use where both high strength and corrosion resistance are necessary.

The copper content ofthe present alloy exerts an important influence upon the hardness as cast or after annealing and upon the age hardening,

which can be induced by reheating or slowlyk palladium, about 29 atomic per cent (45.7 Aweight YAYpercent) gold, about 29. atomic per cent (2,5.0

weight percent) silver and about 19 atomic per cent (9.7 weight'percent) copper developed a 50 hardness of about 144 Brinell as cast, which was reduced to about 133 when annealed and was increased to 238 when reheated and aged. On increasing the copper content to about 28 atomic per cent (14.7 weight percent) and reducing the silver content a proportionate amount, the alloy developed a hardness of, about 169 Brinell when cast, which was reduced to about 159 when an- K a casting alloy, but also increase the oxidation during melting. Care should be exercised in adding increased. amounts of copper because excessive quantities tends vto cause brittle'ness.` The copper content may range between about 16 to '38 atomic per cent (7.84 to 23.68 weight percent) but is preferably held between the limits of 20 to 30 atomic per cent (10.40 to 17.17 Weight percent). It has been found that about 25 atomicl per cent (about 14 weight percent) is nearly the optimum where high strength and ductility are required.

It .is likewise generally desirable to introduce a small amount of a degassier, such as zinc, to render more easy the production of castings. It should be noted, however, that zinc also hardens the alloy, and if present in excessive amounts, .results in undue brittleness.' A further disadvantage of excessive quantities of zinc arises from its volatilization' during melting, which in turn results in achange in the properties of the alloy. I have also found that the alloys containing excessive quantities of zinc tenduto become very hard and brittle when cooled in the mold. For these reasons, I find it' best to limit the zinc content to about 3 atomic per cent (about 2.0 weight percent), and in compounding the alloy, to formulate the proportions so that the zincreplaces an equal amount of copper.

Small amounts of deoxidizing or desulphurizing elements may likewise be employed alone or in conjunction with zinc to facilitate the production of sound, ductile castings. Of these, manganese, magnesium, barium, calcium, boron, silicon, and phosphorous, are the most useful.- Manganese is the least effective, and likewise exerts the least effect upon the alloy, and may be` added in amounts of the order of about 0.2%. Magnesium is powerful and about 0.05 to about 0.1% is about all that can be practically employed. The same rule applies to the last four elements noted. The last three elements are deoxidizers only and must be used with caution to avoid the production of appreciable quantities of low melting phases, which give rise to hot shortness iny the" alloy. Very small amounts of special elements may be added to refine the grain of the cast alloy. f these, rhodium and ruthenium in amounts of the order of about 0.1% have been found effective.

Silver constitutes substantially the remainder 'of the new alloy, aside fromuminor impurities. 'I'he percentage of this metal istermined by the content of the aforementioned constituents to` wit: gold, palladium, copper, plus small amounts' of such densifyihg or deoxidizing or grain refining elements as may be present.

The new alloy is responsive to heat treatment and may be softened by heating to about 700- 750 C. and quickly cooling. The alloy, after being thus softened, may be hardened by re-heating for 5-15 minutes at a temperature of 350- 450.C., or by reheating to 450 C. and then slowly cooling the alloy. An alloy containing 25 atomic per cent (42.3 weight percent) gold, 25 atomic per cent,(22.9 weight percent) palladium, 29 atomic percent (15.7 Weight percent) copper, 1 atomic percent (0.6 Weight percent) zinc, with silver the remainder, showed a tensile strength of 87,000 pounds per square inch, and an elongation of 30% when annealed at 700 C. and quenched, while the same annealed alloy after reheating at 450 C. for 15 minut-es showed a tensile strength of 147,000 pounds per square inch, and an elongation of about 8%, whereas slow cooling the alloy from 450 C. resulted in a tensile strength of 139,000 pounds per square inch and an elongation of about 6%. An alloy containing about 20 atomic percent (34.5 weight percent) gold, about 20 atomic percent (18.6 weight percent) palladium, about 25 atomic percent (14.0 weight percent) copper and about atomic percent (32.9 weight percent) silver'de veloped aha-rdness of about 178 Brinell as cast, which dropped to about 159 when annealed and was increased to about 295 when reheated and aged. A similar alloy containing about 20 atomic o rcent (34.6 weight percent) gold, about 20, atomic percent (18.7 weight'percent) palladium, about 25 atomic percent (14.0 weight percent) copper, about 34 atomic. percent (32,2 weight percent) silver and about 1 atomic percent (0.6 weight percent) zinc, developed a hardness of about 304 Brinnel as cast, which was reduced to about 244 when annealed and was increased to about 358when reheated and aged.

I have likewise discovered that the alloys containing less than 40 atomic percent (about 53.5

. weight percent) of gold plus palladium, with copdevelops a hardness of 155 when annealed at 700 C. and quenched, while the hardness is increased vto 260 Brinell by quenching from 800 C.

` The liquidus and solidus of the new alloy may be variedover a considerable range, particularly by, altering the content of the palladium 'and copper. .Increasing the former raises the melting point, while increasing the latterdecreases it. It is important to note that the spread between the liquidus and solidus is moderate, which is -not -the case with alloys of high platinum content.

This small spread and the convenient melting point of the new alloy give rise to maximum castability. The general relation 'between liquidus and solidus is apparent from the behavior of an alloy containing 25 atomic per cent (22.9 weight per cent) palladium and 25 atomic per cent (42.3

.'Weght per cent) gold with 29 atomic per cent (15.7 weight percent) copper and 1 atomic per cent (0.6 weight per cent) zinc, with silver constituting vsubstantially the remainder, in which `the solidus was found to be located at 1000 C.,` while the liquidus was 1083( C. With the atomic 75 copper content of 25 atomic per cent (about 14.0

weight per cent), the liquidus will decrease as the amount of gold plus palladium is reduced, and' will be 1020 C. with 40- atomic per cent (about 53.5 weight per cent) gold plus palladium, and about 950 C. at 30 atomic per cent (about 42.5 .Weight per cent) gold plus palladium. l

The new alloy, in contrast to alloys of the palladium-silver-copper series, is substantially re- .sistant to nitric acid if the gold content is 15 atomic per cent (about 25.0 weight per cent) or more.v This is a ,matter of great importance as a nitric acid pickle is used by the technicians to remove base metals, etc., from dental castings.

f The tarnish resistance of the new alloy .has been found to be far in excess of that of a goldsilver-copper alloy containing an equal atomic per cent of gold, while if compared on the basis of equal cost the new alloy shows an even greater superiority.

It is to be observed that the present invention provides an alloy comprising about 16 to about 38 atomic per cent (7.84 to 23.68 weight per cent)4 of copper, 'about 30 to about 55 atomic per cent (38.9' to 73.7 weight per cent) of goldl plus palladium, the ratio of palladium to the sumv of gold and palladium expressed in atomic per cent ranging from 0.40 to. 0.58 (or in weight,

percentage ranging from-0.26 to 10.43), and silver constituting substantially the balance.

It is also tov be noted that the present inven- 3"-'l'tion providesvan alloy comprisingfabout 20 to about atomic per cent (10.4 to' 17.17 weight per cent) of copper, about 42 to about 48 atomic per .cent (53.6 to 63.7 weight per cent) of gold plus palladium, the ratio of palladium to the sum of i gold and palladium expressed in atomic per cent ranging from 0.45 to 0.55 (or in AWeight percentage ranging from 0.30 to (W), and silver constituting substantially the balance.

Furthermore, the present invention providesk an alloycomprising about 25 to about 30 atomic per cent (13.47 to 17 .9 5 weight per cent1 of copper, about 30 to about 40 atomic per cent (41.0 to 55.6 weight per cent) of gold plus palladium, the ratio of palladium to the sum of gold and palladium expressed in atomic per cent ranging from 0.40 to 0.5 (or in weight percentage ranging from 0.26

t 0.40) and silver constituting substantially the balance.

"I'he invention further contemplates the pro-r vision of an alloy comprising about 20 to about 30 atomic per cent (10.2 to 16.32 weight per centi) drawings, it will be noted that the new palladium dental alloys are bounded by thequadrlateral mark A-B-C-D. The approximate percentages of the corners of the quadrilateral expressed in weight percentages of gold, of, paladlum and of silver plus copper are set forth in the IolloW-' ing schedule: The weight percentages of `silver and copper are in accordance with the foregoing specification.

Schedule A- B C D Au 29.3' 00.5 40.0 21.4 Pd-; 10.0l 14.1 30.0 10.0 Ag-l-Cu 60.1 25.4 28.5 02.6

In Fig'. 2, I have plotted the new palladium dental alloys on the basis of atomic percentages..

It will be noted that the quadrilateral E-K- L-Q is sub-divided into several smaller quadrilaterals. Thus, the area E-F-P-Q embraces those alloys which are preferably used for casting purposes, although it is to be understood that they may be employed-for other uses. The area G-H-N-O embraces vthose alloys which have 288 30 las Au..y 17. 6

I claimz- 1.*An alloy comprising about Y7.8 to about 23.7' per cent of copper, aboutll to about 30.6 per cent of palladium, about 22.2 to about 54.2 per cent gold, the ratio of palladium to gold expressed in weight percent ranging from 0.36:1 to 0.74:1, and silver constituting the-balance of the alloy and being present in amount of about 52% to about 6.3%. y

2. An alloy comprising about 10.4 to about 17.2% copper, .about 16.9 to aout 24.9 per cent of palladium, about 32.3 Vto about 44.2 per cent of gold', the ratio of palladium to gold expressed in weight per cent ranging from 0.44:1 'to 0.66:1,

l and silver constituting' the balance -of the alloy.

3. An alloy comprising about 13.8 to about 1810- per -cent copper, about 11.5 to about 21.3

per cent palladium, about 24.7 to about 40.9 per palladium, about 37.6 to about 49.2 per cent gold, I

the ratio of `palladium to gold expressed in weight per cent ranging from 0.44: 1 to.0.66:1, and silver constituting the balance of the alloy.

EDMUND M. WISE. 

